Impact of urban forest structure, native species diversity, and vegetation community on invasive plant species richness

Invasive plants have spread across the urban forests in South Korea, resulting in several harmful effects. Socioeconomic aspects of urban environments make urban forests susceptible to invasion. The invasion resistance of the environment is determined by various factors, including native species richness and forest structure; however, this relationship is relatively understudied in urban forests. In this study, we investigated the relationships between invasive plant species richness and different variables, including urban forest structure, native species diversity, and vegetation communities in the urban forests of South Korea, Busan. We investigated these relationships using a stepwise generalized linear model (GLM) and random forest (RF) methods. We used the TWINSPAN method to classify the vegetation communities, and non-metric multidimensional scaling (NMDS) ordination to determine whether certain vegetation communities were prone to invasion. The results showed a weak positive correlation with 0.09 R² value between the richness of invasive species and native Margalef species richness. Native Margalef species richness was also the most important variable showing positive relationship in both GLM and RF. Proximity to human disturbances increased the richness of invasive species, but forest structure had little influence. Ordination showed that no certain community type was susceptible to invasion. These results were due to the afforestation history of the study area and the shade-tolerant characteristics of the invasive species. Because urban forests in South Korea are under increasing environmental stresses, a persistent invasion is expected in the future and require management strategies to maintain the ecosystem services.